The present invention relates to an improved structure and method for facilitating the connection of a small diameter shaft to a substantially larger rotor having a bore into which the shaft extends. One of the important uses for the invention is in providing a connection between a centrifuge rotor and the spindle which drives it.
Centrifuge rotors are normally driven with very small shafts, or spindles, in order to minimize vibration problems at the extremely high speeds required. Significant manufacturing and structural problems are encountered in connecting the ends of such a spindle to the much larger diameter structures located at its opposite ends, the centrifuge rotor at one end, and the driving motor at the other end.
The present invention was developed for the purpose of providing a torque-transmitting connection between a spindle and a substantially larger diameter bore in a motor-driven shaft. However, the invention may be useful wherever a similar problem is encountered.
There are many possible ways of connecting shafts of different diameters, but they each have certain deficiencies. The available ways include: (1) using a "heavy" press fit; (2) using a set screw; (3) assembling with cements of various types; (4) using tapered connections; (5) soldering a hub end to the spindle and fitting it over the motor shaft; and (6) forming "self-collets" by boring or slitting and providing clamping means.
The press fit requires extreme tolerance control. The set screw also has tolerance problems, although less severe; and it also is difficult to manufacture and prone to severe "fretting" corrosion. Cemented assemblies suffer from reliability problems, creating severe requirements during the assembling stage. Tapered connections are inherently quite expensive. Use of a hub end fitting over the motor shaft places limitations on heat treatment of the shaft material and uses up valuable vertical space. And the "self-collets" tend to create operating difficulties and to have "fretting" failure.
The purpose of the present invention is to provide a spindle-to-bore connection which avoids the deficiencies discussed above, and which has, to a significant extent, the virtues of:
(a) Relatively inexpensive manufacture because of ease of assembly and avoiding tolerance problems;
(b) Ready adaptability to different dimensional requirements and to the use of different materials in the spindle, the rotor, and the interconnecting means; and
(c) Functional reliability because of an effective torque-transmitting capability.